Nearly all pushrod-style engines over the last twenty years use a hydraulic roller camshaft because it's the best way to achieve a wider torque band in popular small blocks and big blocks. A roller camshaft's ability to quickly open/close valves allows for more advanced cam profiles while a hydraulic lifter body eliminates the need to constantly set valve lash. These cams also have exceptional "flat" power curves and are often retrofitted into older engines.